The surface structure of a component or a material is an important quality feature in many technical areas.
There are thus different roughness measurement apparatuses for detecting the roughness or roughness depths of surfaces. A sensor tip is typically guided over the surface in mechanical scanning. The result is a height signal recorded over the scanning path, which is also known as surface profile.
Skid probes 1 are known, as are schematically shown in FIG. 1A. A skid probe 1 comprises a skid 2, which depending on the application has a large or small radius and which is used as a sliding element. The sensor tip 4 of a sensor 3 rests with the skid 2 on a surface F to be measured and detects with the sensor tip 4 the surface profile relative to the path of the skid 2. The skid 2 follows the macroscopic unevenness on the surface F, i.e. the undulation and the macroscopic shape. The sensor tip 4 on the other hand detects with its small tip radius the surface roughness and detects grooves for example which were bridged by the skid 2 because it has a far greater effective radius. The skid 2 thus acts in the manner of a mechanical high-pass filter.
FIG. 1B shows the scanning result of a skid probe 1 of FIG. 1A in the schematic form. The behavior in front of an elevation on the surface F for example is characteristic for a skid probe 1. The skid probe 1 is drawn over the surface F and therefore the skid 2 reaches this elevation before the sensor tip 4. The entire sensor 3 is thus lifted and the sensor tip 4 then protrudes further downwardly from the surrounding sensor housing. This is recorded in a manner (see region B1 in FIG. 1B) as if the sensor tip 4 would apparently run in a depression of the surface F.
An improved skid probe is known from the published patent application WO2010079019A2. Said skid probe is shown in FIG. 2A in a respective functional view. In order to allow a comparison of the improved skid probe of FIG. 2A with the solution of FIG. 1A, the same reference numerals were used in this case. The sliding element 2 is arranged at the extremal end of a sensor pin. The sensor tip 4 is arranged in the sensor pin, wherein the distance A between the sliding element 2 and the sensor tip 4 is fixedly predetermined.
A further exemplary skid probe 1 is shown in FIG. 2B. The skid probe 1 of FIG. 2B is based on the fundamental principle of FIG. 2A. Other than in FIG. 2A, the sequence of the sensor tip 4 and the sliding element 2 is reversed. In the example shown in FIG. 2B, the sensor tip 4 is situated before the sliding element 2. In this case too, the distance A between the sliding element 2 and the sensor tip 4 is fixedly predetermined.
Skid probes can partly supply distorted results. This is the case for example if the movement of the skid 2 overlaps constructively with the movement of the sensor tip 4 and an output signal is supplied which is too high, or if the movements cancel each other out entirely or in part and thus supply a signal which is too low.
Other problems occur for example when measuring the surface properties of tooth flanks. On the one hand, current skid probes are not capable of entering far into the tooth gaps of small-module gearwheels. On the other hand, the sliding element 2 runs free when the tooth crest of a tooth flank is reached. As a result, the topography of tooth flanks cannot be measured close to the tooth crest. A solution according to FIG. 2A is not suitable because the sensor tip 4 runs empty upon reaching the tooth crest. In a solution according to FIG. 2B on the other hand, the skid 2 would run free upon reaching the tooth crest.